Biological and Environmental Research - Earth and Environmental System Sciences
Earth and Environmental System Modeling

Attribution of NAO Predictive Skill Beyond 2 Weeks in Boreal Winter

TitleAttribution of NAO Predictive Skill Beyond 2 Weeks in Boreal Winter
Publication TypeJournal Article
Year of Publication2020
JournalGeophysical Research Letters
Volume47
Number22
Abstract / Summary

Weeks 3–6 averaged winter North Atlantic Oscillation (NAO) predictive skill in a state‐of‐the‐art coupled climate prediction system is attributed to two principle sources: upper and lower boundary conditions linked to the stratosphere and El Niño‐Southern Oscillation (ENSO), respectively. A 20‐member ensemble of 45‐day reforecasts over 1999–2015 is utilized, together with uninitialized simulations with the atmospheric component of the prediction system forced with observed radiative forcing and lower boundary conditions. NAO forecast skill for lead times out to 6 weeks is higher following extreme stratospheric polar vortex conditions (weak and strong vortex events) compared to neutral states. Enhanced weeks 3–6 NAO predictive skill for weak vortex events results primarily from stratospheric downward coupling to the troposphere, while enhanced skill for strong vortex events can be partly attributed to lower boundary forcing related to the ENSO phenomenon. Implications for forecast system development and improvement are discussed.

URLhttp://dx.doi.org/10.1029/2020gl090451
DOI10.1029/2020gl090451
Journal: Geophysical Research Letters
Year of Publication: 2020
Volume: 47
Number: 22
Publication Date: 11/2020

Weeks 3–6 averaged winter North Atlantic Oscillation (NAO) predictive skill in a state‐of‐the‐art coupled climate prediction system is attributed to two principle sources: upper and lower boundary conditions linked to the stratosphere and El Niño‐Southern Oscillation (ENSO), respectively. A 20‐member ensemble of 45‐day reforecasts over 1999–2015 is utilized, together with uninitialized simulations with the atmospheric component of the prediction system forced with observed radiative forcing and lower boundary conditions. NAO forecast skill for lead times out to 6 weeks is higher following extreme stratospheric polar vortex conditions (weak and strong vortex events) compared to neutral states. Enhanced weeks 3–6 NAO predictive skill for weak vortex events results primarily from stratospheric downward coupling to the troposphere, while enhanced skill for strong vortex events can be partly attributed to lower boundary forcing related to the ENSO phenomenon. Implications for forecast system development and improvement are discussed.

DOI: 10.1029/2020gl090451
Citation:
Sun, L, J Perlwitz, J Richter, M Hoerling, and J Hurrell.  2020.  "Attribution of NAO Predictive Skill Beyond 2 Weeks in Boreal Winter."  Geophysical Research Letters 47(22).  https://doi.org/10.1029/2020gl090451.